The present invention is in the field of filament winding, more particularly, the invention relates to a combination of filament winding and rotational molding.
Filament wound articles and methods of filament winding are described by Rosato and Grove, Jr., Filament Winding, Interscience Publishers, John Wiley & Sons, Inc., (Copyright 1964). This text discloses the development, manufacture, applications, and design relating to filament winding. Briefly, the process of filament winding comprises winding filamentous nonmetallic or metallic materials in fibrous or tape form continuously on a form or mandrel which shape corresponds to the inner structure of the part being fabricated. Generally, the filaments in whatever form are encased in a resin matrix. The filaments are either wetted out immediately before winding or impregnated ahead of time. The resin contains the reinforcement, holding it in place, sealing it from mechanical damage, and protecting it from environmental deterioration. Where the resin is a crosslinkable resin, the filament wound article is crosslinked or cured. After curing the form may be removed, discarded, or used as an integral part of the structural item.
Filament winding is carried out on specially designed automatic machines. There is precise control of the winding pattern and the direction of the filaments as required for maximum strength. This winding pattern can only be achieved with controlled machine operation, which can be computer controlled. Filament winding results in a strong, lightweight part.
Filament winding is useful to make hollow enclosed articles having high strength and lightweight. It is known to blow-mold small tanks from polymers such as polyethylene and filament wind the tanks. These small tanks have been used as lightweight air tanks which can be carried on the back of a person such as a fireman. Injection molded parts have been fused together to form enclosed articles such as pool filters. These pool filters have been filament wound.
In certain applications, it is known to use a liner material inside of the filament wound structure. This material has been applied around the mandrel prior to the wrapping operation. The inner liner has been used as a insulator and can be made of a rubber-plastic sheet or reinforced plastics.
A method of filament winding of particular interest is integral case winding. In this process, rocket propellent castings are completed by filament winding to form an integral filament wound rocket motor case.
Although the above discussed methods of filament winding are useful, they have certain limitations. For example, filament winding of blow molded enclosed polyethylene tanks can only be used to produce tanks of sizes and shapes limited to blow molding operations. Further, in blow molding, the blow molded article has a non-uniform cross sectional wall thickness. Enclosed articles produced by fusing together of injection molded parts require the step of fusing or adhesively bonding together the various parts with the inherent risk of failure at the seams.
Rotational molding, also known as rotomolding, is used in the manufacture of hollow objects from thermoplastics. In the basic process of rotational molding, solid or liquid polymers are placed in a mold. The mold is first heated and then cooled while being rotated about two perpendicular axes simultaneously. Many polymers can be used in the rotational molding process. Popular polymers for this use are polyolefins such as polyethylene. It is also known to use polycarbonates, crosslinkable polyethylene, nylon, and other materials. In selecting the rotational molding grade formulation, care must be taken to assure that there will not be thermal degradation during the heating cycle. A general discussion on rotational molding is given in MODERN PLASTICS ENCYCLOPEDIA 1979-1980, Volume 56, No. 10A, beginning at Page 381.